JPS5819377B2 - Sand molds or cores and their processing methods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to sand molds or cores, in particular to foundry sand molds or cores, and methods of processing them.

Until now, sand molds or cores have been manufactured using foundry sand and synthetic organic resins, water glass, clay, etc. as binders.

However, in the method of using synthetic organic resin, especially thermosetting resin, after molding a sand mold or core, pouring the mold, using the combustion residual carbon of the synthetic organic resin from the molten metal as a binding medium, and retaining the shape after pouring. However, the strength of the sand mold was not sufficient, especially
The area near the contact surface between the molten metal and the sand mold or core was fragile due to severe combustion of the residual carbon of the synthetic organic resin due to oxidation.

On the other hand, when sand molds or cores are formed using water glass, the water glass melts during pouring, and the foundry sand and water glass fuse to the cast iron, reducing product value. It required a lot of effort.

Furthermore, when clay is used, the strength of the sand mold or core is generally weak, and improvement has been desired.

The present inventors improved the strength, particularly the surface strength, of sand molds or cores, and prevented the oxidation of residual carbon after combustion of synthetic organic resins.
In addition, to prevent water glass from fusing, apply an aluminum phosphate solution to the surface of the sand mold or core after molding, and apply a
I found out that drying at temperatures above 500°C was sufficient.
Drying at high temperatures such as °C is not economical due to drying costs.

Therefore, when drying at 500° C. or lower, the aluminum phosphate coating absorbs moisture during storage of the sand mold or core, and the moisture absorbed in the coating transfers into the molten metal, causing a so-called blotting phenomenon.

To solve this problem, we used an aluminum phosphate solution in which a small amount of magnesia was suspended in place of the aluminum phosphate solution. Although the hygroscopicity was improved, the film-forming ability was large and it was difficult to form a film on the surface of the sand mold or core. It was found that the coating formed a smooth coating film and had poor adhesion to the coating material.

Therefore, if you apply magnesia slurry to the sand mold or core after molding, and then apply aluminum phosphate solution,
The present invention was completed based on the discovery that even when dried at a low temperature of about 200° C., the hygroscopicity is extremely low and the adhesion to the mold material is good.

That is, the first invention relates to a sand mold or core whose contact surface with bath water is made of a coating system consisting of an electrofused magnesia layer and an aluminum phosphate layer, and the second invention relates to a sand mold or core whose contact surface with bath water is made of a coating system composed of an electrofused magnesia layer and an aluminum phosphate layer. The present invention relates to a method for treating sand molds or cores, which comprises separately applying an organic solvent-based electrofused magnesia slurry and an aluminum phosphate solution to the sand mold or core.

As the sand for the sand mold or core used in the present invention, silica sand,
Medium acidic sand such as zircon sand and chamotte can be used, and among them, silica sand is most desirable in consideration of reactivity with the aluminum phosphate solution.

Now, the binding materials used to manufacture sand molds or cores include synthetic organic resins such as phenol formaldehyde, urea formaldehyde, and furan resin.
Examples include water glass, clay, and cement.

Magnesia slurry is then applied to the surface of the sand mold or core molded by a conventional method, but the application method varies depending on the size and shape of the sand mold or core.

Any suitable method may be used, and generally, spraying with a spray gun, brushing, dipping a sand mold or core in magnesia slurry, etc. are employed.

Although it is related to the particle size of the sand used in the sand mold, the electrofused magnesia should generally have a particle size (L15 mr/L or less).

Magnesia is made into a slurry to make it easier to apply it to sand molds or cores.As a medium, organic solvents with lower boiling points are preferable, such as methanol, ethanol, acetone, etc. Among them, from the viewpoint of environmental hygiene and economy, Alcohol is preferable, and the slurry concentration may be adjusted to the optimum concentration depending on the coating method employed.

The amount of coating varies depending on the Al2O3/P2O6 molar ratio of the aluminum phosphate to be applied next, but it is preferably applied so that the MgO/P2O5 molar ratio is approximately within the range of 0.2 to 1.5.

Note that the sand mold or core after applying the magnesia slurry may be dried, but may be undried.

In the present invention, an aluminum phosphate layer is further formed on the magnesia layer, and this aluminum phosphate layer formation is performed by applying an aluminum phosphate solution, and the application method is the same as that for forming the magnesia layer. method can be adopted.

The composition of the aluminum phosphate solution used here is A
A l2O3/P2O5 molar ratio of 0.25 to 0.43 is preferable.

That is, when the upper limit is below, the penetration of aluminum phosphate into the sand mold is small and the reinforcing effect is poor, while when the lower limit is below, the aluminum phosphate and magnesia react, and the hygroscopicity is extremely reduced when heated to about 200°C. This makes it more likely that the dandruff phenomenon will occur.

Therefore, the solid content concentration of the aluminum phosphate solution is preferably in the range of about 10 to 60% by weight.

The solid content concentration of the present invention is expressed in weight % when the solution is dried at 110° C. and reaches a constant weight.

By the way, if it exceeds 60% by weight, the permeability into the sand mold will deteriorate and a coating film will be formed on the surface of the sand mold, resulting in a reduction in the reinforcing effect of the sand mold surface and poor adhesion with the mold coating material.

On the other hand, if it is significantly less than 10% by weight, a large amount of energy is required to dry the aluminum phosphate solution, which is not economical.

The aluminum phosphate solution in the present invention refers not only to a pure aluminum phosphate solution but also to a solution containing metals such as sodium, potassium, iron, magnesium, nickel, and chromium.

Now, the aluminum phosphate solution applied in this way is then subjected to a drying step. Regarding the drying temperature and time, it is desirable to dry it for 20 minutes or more at 200° C., for example.

That is, drying at 200° C. or lower cannot sufficiently prevent hygroscopicity even if drying is carried out for a long time.

The present invention follows the above steps to first form an fused magnesia layer and then an aluminum phosphate layer on the surface of the sand mold or core, but by forming two layers on the surface of the sand mold or core, the organic It is possible to prevent the oxidation of residual carbon in the resin and the fusion of water glass, and furthermore, it is possible to increase the strength of the sand mold surface by the binding action of aluminum phosphate.

The present invention will be further explained below with reference to Examples.

In the following examples, unless otherwise specified, percentages and parts are expressed in weight units.

Example 1 Sand mold of silica sand coated with furan resin (50φx5
0mm) to electrofused magnesia (particle size 0.088mm or less)
About 1.5 g of 20% ethyl alcohol suspension was sprayed with a spray gun, and then aluminum phosphate solution (A1
203/P2O5 molar ratio 0.33, solid content concentration 50%)
Spray about 4g with a spray gun and apply molding material (
The main component was bentonite).

(Example of the present invention) Comparative example 1 In the sand mold of Example 1, 25 parts of a 20% aqueous solution of electrofused magnesia (particle size 0.088 u or less) and an aluminum phosphate solution (
A1203/P2O5 molar ratio 0.33, solid content concentration 50
%) was mixed in advance with a spray gun, and the coating material was brushed on top of the mixture.

Comparative Example 2 The sand mold of Example 1 was coated with aluminum phosphate bath solution (A1203
/P2O6 molar ratio 0.33, solid content concentration 50%) approx. 4g
Next, about 1.5 g of a 20% ethyl alcohol suspension of electrofused magnesia (particle size of 0,088 mm or less) was sprayed on the surface of the mold, and a molding material was brushed on top of the spray.

These test pieces were dried at 200° C. for 60 minutes, and a moisture absorption test was performed, and the adhesion of the coating material and the layer thickness of aluminum phosphate were measured, and the physical properties thereof were evaluated.

The results are shown in Table 1.

Moisture Absorption Test The specimen was left for 24 hours while the humidity was adjusted to 85% RH, and its moisture absorption rate was measured using the following formula.

Adhesion of mold coating material The mold coating material on the specimen was rubbed five times with a scrub brush, and those that adhered to the specimen and remained were evaluated as good, and those that hardly remained were evaluated as poor.

Measuring the layer thickness of aluminum phosphate Scrape the side of the specimen with a wire brush, and the remaining hard part is where the aluminum phosphate has penetrated and hardened.
The layer thickness was measured at four points with a caliper, and the average value was calculated.

Example 2 Approximately 2.0 g of a 10% methyl alcohol suspension of each additive-free substance listed in Table 2 was sprayed onto the sand mold of Example 1 using a spray gun, and then an aluminum phosphate solution (A1203/P2O
(MgO/P2O5 molar ratio 0.33, MgO/P2O5 molar ratio 0.1, solid content concentration 50%) was applied by brushing.

These test pieces were dried at 200°C for 60 minutes.
The moisture absorption rate and the layer thickness of aluminum phosphate were measured.

As is clear from Table 2, additives other than fused magnesia have high reactivity with aluminum phosphate, and when an aluminum phosphate solution is applied, they react violently, thicken, and significantly reduce penetration into the sand mold. In addition, unreacted aluminum phosphate that does not permeate into the sand mold remains, resulting in a high moisture absorption rate.

In other words, it is understood that electrofused magnesia imparts much superior properties compared to other additives.

*20% of fused magnesia (particle size 0.088 mm or less) dispersed in the solvent shown in Table 3 in the sand mold of Example 1.
Approximately 1.5 g of the suspension was sprayed with a spray gun, and then an aluminum phosphate solution (A1205/P2O5 molar ratio of 0
．． 4. Approximately 2.5 g of solids concentration 50% was brushed on.

These test pieces were dried at 200° C. for 30 minutes and 60 minutes, and their loss on drying and surface condition were tested.

The results are shown in Table 3. From the above table, it can be seen that organic solvents are easy to dry and the surface condition is extremely good.

Example 4 Electrofused magnesia (particle size 0.088 mw) was added to the sand mold of Example 1.
Approximately 1.0 g of a 20% ethyl alcohol suspension of 20% ethyl alcohol (A1203/P2O5 molar ratio 0.4, solid content concentration 4
Approximately 2.0 g of 0%) was brushed on, and a molding material was brushed on top of that, followed by drying at 200° C. for 1 hour.

As a result, aluminum phosphate easily penetrates into the sand mold,
Adhesion to the coating material was also good.

When approximately 1.3 g of aluminum phosphate solution (A1203/P2O5 molar ratio 0.4, solid content concentration 65%) is used instead of the above aluminum phosphate solution, the penetration of aluminum phosphate into the sand mold is significantly reduced. The adhesion of the coating material deteriorated.

Furthermore, aluminum phosphate solution (klj20sl P2O
5 molar ratio 0.4, solid content concentration 5%)], aluminum phosphate penetrated well into the sand mold, but the surface of the sand mold was not dried.

Example 5 Using a sand mold coated in the same manner as in Example 1, 110'C,
, 200°C, 300°C, and 400°C for 10 to 240 minutes, and the surface condition and moisture absorption rate of the sand molds were investigated.

The results are shown in Table 4. Example 6 Sand mold of silica sand coated with phenolic resin (50φ
About 1.0 g of a 20% acetone suspension of electrofused magnesia (particle size 0.088 mm or less) was sprayed onto the aluminum chromium phosphate solution (A1
203/P2O5 molar ratio 0, 33, Cr2O5/
P2O5 molar ratio 0,065, solid content concentration 15%) approx. 6.
0g was brushed on, and the molding material was brushed on top of it.

This test piece was dried at 200° C. for 60 minutes, and its moisture absorption rate was measured to be 2.9%.

Example 7 Instead of the chromium aluminum phosphate solution in Example 6, an iron aluminum phosphate solution (k1203/P205 molar ratio Q, 25, Fe2O3/P2O5 molar ratio 0.12) was used.
, solid content concentration 35%) was tested in the same manner as in Example 6, and the moisture absorption rate was 4.2%.

Example 8 Sand mold (50φ x 50++ m) of silica sand coated with urea formaldehyde resin in a 10% ethyl alcohol suspension of electrofused magnesia (particle size 0.088 mm or less)
and then soaked in aluminum phosphate solution (A1203
/P2O5 molar ratio 0.10, solid content concentration 48%), aluminum phosphate solution (A1203/P2O5 molar ratio 0.33, solid content concentration 5)
0%) and aluminum phosphate solution (A1203/P2O5 molar ratio 0.48, solid content concentration 5
Approximately 3.0 g of 4%) was brushed on each.

These test pieces were dried at 200° C. for 60 minutes, and the moisture absorption rate and aluminum phosphate layer thickness were measured.

The results are shown in Table 5. Example 9 A 10% ethyl alcohol suspension of electrofused magnesia (particle size of 0,088 mm or less) was uniformly sprayed onto a furan resin-coated silica sand mold using a spray gun, and then an aluminum phosphate solution (M203/P2O5 molar ratio of 0 ．．
33, solid content concentration 40%) was sprayed with a spray gun until it penetrated approximately 4 to 5 mm, and the coating material was brushed on top of it.

After drying this sand mold by heating it with a gas burner, molten metal was poured into it.

As a result, the cast iron obtained had no internal defects such as blisters, and the surface of the sand mold was considerably blacker and had more residual carbon from the furan resin than when the mold material was simply brushed onto the sand mold. .

Claims (1)

[Scope of Claims] 1. A sand mold or core whose contact surface with molten metal is made of a coating system consisting of an electrofused magnesia layer and an aluminum phosphate layer. 2. The sand mold or core according to claim 1, wherein the aluminum phosphate has an A1□Os/P2O5 molar ratio of 0.25 to 0.43. 3 MgO/P2O5 molar ratio of coating system is 0.2 to 1.5
A sand mold or core according to claim 1, which falls within the scope of claim 1. 4. A method for treating a sand mold or core, which comprises separately applying an organic solvent-based electrofused magnesia slurry and an aluminum phosphate solution to the sand mold or core. 5. The method according to claim 4, wherein the organic solvent is alcohol. 6. The method according to claim 4, wherein the aluminum phosphate solution has an Al2O3/P2O5 molar ratio of 0.25 to 0.43. 7 Solid content concentration of aluminum phosphate solution is 10 to 60
5. A method according to claim 4, wherein the amount is % by weight.